Some classics ( my 67 Plymouths for example ) had adhesive backed foam weather stripping laid along there. about 1 inch wide, 1/8th thick.
Dodge and others had a bead of extruded caulk. Both would hold water and cause eventual rust. From what I have seen the narrow of caulk held small pockets of water more than the foam. for example, There's a thread here about flipper/scammer, Duster turned Demon? anyway... in that video the potential buyer pointed out the rust through at about middle of this seam. My 67 Plymouths have no major rust here although they are rusted at other typical locations.
Pull a fender from a much later Ford, Honda, any... you wont find anything more than painted metal bolted to painted metal. There's my sign that mfgrs figured out it wasn't necessary and probably does more harm that good.